The pumping stages for turbomolecular pumps are traditionally composed of pairs of disks, one of which (the stator disk) is integral with the pump body, while the other one (the rotor disk) is integral with a shaft that is centrally placed with respect to the pump body and the stator disk and rotated by a motor.
Both such disks are commonly equipped with blades, the number of which ranges between 20 and 60: these are oriented with opposite blade aspect with respect to the rotation plane, in order to perform pumping of gas molecules with the rotor disk and changing the speed distribution of gas molecules with the stator disk.
In particular, the number of disk blades, and consequently their pitch, generates the capability of compressing gases at a certain speed.
The function of the stator disk is mainly change the speed distribution for gas molecules after they have been pumped by the rotor disk, to be intercepted and pumped by the rotor disk in the following pumping stage.
If the pumping stage lacked a stator disk, the gas molecules would not be pumped by the rotor disk in the following stage; in fact, they leave the rotor disk with a speed distribution whose maximum is next to the opening angle of the rotor that pumped them, and therefore only a negligible portion of these molecules could be intercepted by the following rotor disk.
Since these pumping stages are configured to obtain a high degree of vacuum (that is, very low pressure, the rotor-stator stage efficiency is high only next to low pressure inside the body, that is in extreme rarefaction situations where friction between pumping stage disks and present gas is negligible, while efficiency remains low at the beginning of the evacuation cycle, during which the pump works with viscous gases and the process is governed either by a fore vacuum pump or by possible stages with adequate geometries, integral with the turbomolecular pump shaft.
In the first operating stage of the pump, that is when gas pressure in the body is close to the atmospheric pressure (about 1000 mbar), the presence of a traditional bladed stator disk is therefore disadvantageous, since its deflection function is negligible, while power absorption by friction with present gas is very high.
It has been verified experimentally that a turbomolecular pump having a pumping stage without a stator disk, absorbs, in a steady state rotation, about 17 Watts at 90 Hz and about 50 Watts at 160 Hz, while a pump equipped with traditional stages including bladed stator disks absorbs about 190 Watts at 80 Hz.
The purpose of the present invention is to provide a pumping stage for turbomolecular pumps configured in such a manner as to save the absorbed power during the initial stage of the evacuation cycle without losses in the pumping capacity of the pump itself.
These and other purposes are reached by a pumping stage for turbomolecular pumps comprising a rotor disk and a stator disk integral with the pump body and centrally drilled, characterized in that the stator disk is a disk the surface of which is substantially smooth, said surface being able to assume, during the evacuation cycle, a bladed configuration through lifting its radial sections, said lifting of radial sections being controlled by at least one operating mechanism.